Mononuclear and Dinuclear Nickel Sites on Periodic Mesoporous Silica for CO2 Cycloaddition to Epoxides

The development of efficient heterogeneous catalysts for converting carbon dioxide into value-added products under mild conditions remains an important challenge. Herein, we report the synthesis of mono- and dinuclear Ni-functionalized materials through stepwise grafting onto periodic mesoporous silica (SBA-15). The materials were systematically constructed via aminosilane functionalization, ligand immobilization, and subsequent coordination of Ni centers, and were comprehensively characterized by several techniques, including PXRD, SEM/TEM, EA, ICP-OES, DRIFT-IR, N2 physisorption, XPS, and solid-state MAS NMR, confirming the successful formation of well-defined surface-bound Ni species. The resulting catalysts were evaluated for the cycloaddition of CO2 to epoxides. The immobilized dinuclear nickel naphthyridine diimine material (Ni2-NDI@SBA-15250) exhibited superior catalytic performance compared with its mononuclear nickel phenanthroline-derived analogue (Ni-PhenDI@SBA-15250) and the corresponding homogeneous systems, achieving high to full conversions and >99% selectivity under relatively mild conditions (80 °C, 10 bar CO2) with only 0.1 mol % Ni. The enhanced activity is consistent with cooperative interactions between adjacent Ni centers, combined with the confinement effects of the ordered mesoporous structure. Furthermore, the catalyst demonstrated good stability and recyclability, with negligible metal leaching as confirmed by hot filtration and ICP analysis. This work highlights the potential of heterogenizing multinuclear Ni complexes within mesoporous frameworks for efficient CO2 utilization and provides insight into the design of robust heterogeneous catalysts for sustainable transformations.